Microcapsular opacifier system

ABSTRACT

D R A W I N G OPACIFIERS COMPRISING AIR-CONTAINING MICROCAPSULES HAVING AN AVERAGE PARTICLE DIAMETER OF BELOW ABOUT ONE MICRON PROVIDE HIGHLY OPAQUE SURFACES WHEN COATED ONTO AND/OR INCORPORATED INTO FIBROUS AND NON-FIBROUS SUBSTRATES. THE OPACIFIERS ARE PRODUCED BY HEATING LIQUIDCONTAINING PRECURSOR MICROCAPSULES AT TEMPERATURES SUFFICIENT TO EXPEL THE LIQUID AND PROVIDE AIR IN THE MICROCAPSULE.

June 15, 1971 A. E. VASSILIADES ETAL MICROCAPSULAR OPAC IFIER SYSTEMFiled Dec. 23, 1968 OIL ' BINDER I DRIVE OFF OIL AND COAT 8 Sheets-Sheet1 EMULSIFYING AGENT IN WATER SOLUTION EMULSIFY UNTIL PARTICLE DIAMETERBELOW ONE MICRON AGENT ADD ENCAPSULATING CURE FADBITENAITI DRIVE OFF OILAND ADMIX WITH COATING FORMULATION DRIVE OFF OIL! MIX WITH FIBERS COATAND DRIVE OFF OIL MIX WITH FIBERS,

FORM WEB DRIVE OFF ou AND FORM WEB PRINCIPAL STEPS OPTIONAL STEPSINVENTORS ANTHONY E. VASSILIADES EDWARD F. NAUMAN SHRENIK SHROFF June15, 1971 A. E. VASSILIADES ETAL 3,585,149

MICROCAPSULAR OPACIFIER SYSTEM Filed Dec. 23, 1968 8 Sheets-Sheet zPREPARE A SOLUTION OF A EMULSIFY A WATER- HYDROPHOBIC,THERMOPLASTIC CBLE OILY MA ERIAL IN RESIN IN A WATER-AND OIL- AN AQUEOUS COLLOIDAI-M|SC|BLE ORGANlC SOLVENT SOLUTION OF AN AMPHIPHILIC EMULSIFYING AGENTSLOWLY ADMIX THE RESIN SOLUTION AND THE EMULSION UNDER CONDITIONS OFBRISK AGITATION TO SEPARATE THE RESIN FROM SOLUTION AND ENCAPSULATEMINUTE LIQUID EMULSION DROPLETS COAT THE MICROCAPSULAR DIS- PERSION ONTOA WEB MATERIAL AND DRY PRINCIPAL STEPS OPTIONAL STEPS FIG.2

INVENTORS ANTHONY E. VASSILIADES EDWARD F. NAUMAN SHRENIK SHROFF June15, 1971 VASSILIADES EI'AL 3,585,149

MICROCAPSULAR OPACIFIER SYSTEM Filed Dec. 23, 1968 s Sheets-Sheet sPREPARE A PARTIALLY EMULSIFY A wATER- CONDENSED, AQUEOUS, IMMISCIBLEOILY MATERIAL TH RMO E T RESIN IN AN AQUEOUS COLLOIDAL SYEEUP S SOLUTIONOF AN AMPHI- PHILIC EMULSIFYING AGENT SLOWLY ADMIX THE REsIN SYRUP ANDTHE EMULSION UNDER CONDITIONS OF BRISK AGITATION To 3 PRECIPITATE THERESIN AND ENCAPSULATE MINUTE LIQUID EMULSION oRoPLE s COAT THEMICROCAPSULAR DIS- PERSION ONTO A WEB MATERIAL AND DRY A PARTIALLYCONDENSED, AQUEOUS THERMOSETTING RESIN SYRUP AWATER IMMISCIBLE A DRY P IHILIC OILY MATERIAL EMULSIFYING AGENT I ADMIX TO FORM AWATER-IN-OILEMULSION I SLOWLY ADMIX WATER WITH THE EMUL- SION UNDER CONDITIONS OFBRISK AGITATION TO:

I. INVERT THE EMULSION,

2. PRECIPITATE THE RESIN, AND 3. ENCAPSULATE MINUTE OIL-IN- WATEREMULSION DROPLETS INVENTORS COAT THE MICROCAPSULAR DIS- PERSION ONTO AWEB MATERIAL AND DRY ANTHONY E. VASSILIADES EDWARD F. NAUMAN F I G 4HRENIK SHROFF June 15, 1971 A. E. VASSILIADES ETAL MICROCAPSULAROPACIFIER SYSTEM Filed Dec. 23, 1968 A SOLUTION OF HYDROPHOBICTHERMOPLASTIC RESIN IN A WATER-AND OIL-MISCIBLE ORGANIC SOLVENT A WATERIMMISCIBLE OILY MATERIAL 8 Sheets-Sheet 4 A PARTIALLY CONDENSED,AQUEOUS,THERMOSETTING RESIN SYRUP A DRY AMPHIPHILIC EMULSIFYING AGENTADMIX TO FORM AWATER-IN-OIL EMULSION I SLOWLY ADMIX WATER WITH THEEMULSION UNDER CONDITIONS OF BRISK AGITATION TOZ l. INVERT THE EMULSION,

2. PRECIPITATE BOTH RESINS, AND

3. ENCAPSULATE MINUTE OIL-IN- WATER EMULSION DROPLETS COAT THEMICROCAPSULAR DIS- PERSION ONTO A WEB MATERIAL AND DRY FIG. 5

INVENTORS ANTHONY E. VASSILIADES EDWARD F. NAUMAN SHRENIK SHROFF June15, 1971 5 VASSlLlADEs ETAL 3,585,149

MICROCAPSULAR OPACIFIER SYSTEM Filed DEC. 23, 1968 8 Sheets-Sheet 5 APARTIALLY CONDENSED, AQUEOUS, THERMOSETTING RESIN SYRUP A WATERIMMISCIBLE A DRY AMPHIPHILIC OILY MATERIAL EMULSIFYING AGENT ADMIX TOFORM AWATER-IN-OIL EMULSION SLOWLY ADMIX WATER WITH THE EMULSION UNDERCONDITIONS OF BRISK AGITATION TOI I. INVERT THE EMULSION,

2. PRECIPITATE THE RESIN, AND

3. ENCAPSULATE MINUTE OIL-IN- WATER EMULSION DROPLETS SLOWLY ADMIX ASOLUTION OF HYDROPHOBIC, THERMOPLASTIC RESIN IN A WATER-AND OIL-MISCIBLEORGANIC SOLVENT UNDER CONDITIONS OF BRISK A'GITATION TO SEPARATE THETHERMOPLASTIC RESIN FROM SOLUTION AND ENCAPSULATE THE DISPERSED,THERMOSETTING RESIN MICROCAPSULES COAT THE MICROCAPSULAR DIS- NVENTORSPERSION ONTO A WEB MATERIAL AND DRY ANTHONY E. VASSILIADES EDWARD F.NAUMAN SHRENIK SHROFF June 15, 1971 VASSlLlADEs ET AL 3,585,149

MI CROCAPSULAR OPACIFIER SYSTEM Filed Dec. 23, 1968 8 s t g 6 PREPARE ASOLUTION OF A EMULSIFY AWATER- HYDROPHOBIC, THERMOPLASTIC IMMISCIBLEOILY RESIN IN A WATER-AND OIL- MATERIAL IN A AQUEOUS MISCIBLE ORGANICSOLVENT COLLOIDAL SOLUTION OF AN AMPHIPHILIC EMULSIFYING AGENT SLOWLYADMIX THE RESIN SOLUTION AND THE EMULSION UNDER CONDITIONS OF BRISKAGITATION TO SEPARATE THE RESIN FROM SOLUTION AND ENCAPSULATE MINUTELIQUID EMULSION DROPLETS SLOWLY ADMIX A PARTIALLY CONDENSED,AQUEOUS,THERMOSETTING RESIN SYRUP WITH THE AQUEOUS, MICROCAPSULARDISPERSION UNDER CONDITIONS OF BRISK AGITATION TO PRECIPITATE THETHERMO- SETTING RESIN AND ENCAPSULATE THE DISPERSED, THERMOPLASTIC RESINMICROCAPSULES COAT THE MICROCAPSULAR DIS- PERSION ONTO A WEB MATERIALAND DRY INVENTORS ANTHONY E. VASSILIADES EDWARD F. NAUMAN SHRENIK SHROFFJune E5, 1971 v ss p s EIAL 3,585,149

MICROCAPSULAR OPACIFIER SYSTEM Filed Dec. 23, 1968 8 Sheets-Sheet 7EMULSIFYING AGENTISI IN A WATER-IMMISCIBLE WATER OIL MATERIAL ADMIX WITHSUFFICIENT WATER TO FORM A PRIMARY OIL-IN-WATER CROSS- LINKING ORCOMPLEXING AGENT SLOWLY ADD THE CROSS-LINKING OR COMPLEXING AGENT TO THEEMULSION UNDER CONDITIONS OF BRISK AGITATION TO FORM THE FINALMICROCAPSULES L L l I SEPARATE CAPSULES FROM I I EMULSION BY PHYSICALMEANS:

COAT THE MICROCAPSULAR DISPERSION ONTO A WEB MATERIAL AND DRY INVENTORS8 ANTHONY E. VASSILIADES EDWARD F. NAUMAN SHRENIK SHROFF PRINCIPAL STEPSALTERNATE STEPS June 15, 1971 A. E. VASSILIADES ETAL MICROCAPSULAR OPACIFIER SYSTEM Filed Dec. 23, 1968 EMULSIFYING AGENT(S) IN WATER 8Sheets-Sheet 8 A WATER IMMISCIBLE OILY MATERIAL ADMIX TO FORM WATEREMULSION A PRIMARY OIL- IN STEPS BELOW THIS LINE ARE SAME AS FlG.8

FIG.

INVENTORS ANTHONY E. VASSILIADES EDWARD F. NAUMAN SHRENIK SHROFF UnitedStates Patent 3,585,149 Patented June 15, 1971 3,585,149 MICROCAPSULAROPACIFIER SYSTEM Anthony E. Vassiliades, Deerfield, Edward F. Nauman,Lake Forest, and Shrenik Shrotf, Chicago, Ill., assignors to U.S.Plywood-Champion Papers Inc, New York,

Filed Dec. 23, 1968, Ser. No. 786,337 Int. Cl. B01j 13/02,- (30% /00,-B44d 1/02 U.S. Cl. 252-316 23 Claims ABSTRACT OF THE DISCLOSURE CROSSREFERENCE TO RELATED APPLICATIONS This application contains subjectmatter common to following prior copending applications: U.S. patentapplication Ser. No. 503,391 filed Oct. 23, 1965 now U.S. Patent No.3,418,656; U.S. patent application Ser. No. 503,966 filed Oct. 23, 1965now U.S. Patent No. 3,418,- 250; and U.S. application Ser. No. 583,046filed Sept. 29, 1966.

FIELD OF THE INVENTION This invention relates to a method for providinghigh opacity in fibrous and non-fibrous substrates, surface finishes andto the substrates produced by such method. More specifically, thisinvention relates to microcapsular opacifiers, their production, and theuse of such opacifiers in coatings, substrates and the like.

DESCRIPTION OF THE PRIOR ART The development of fibrous and non-fibroussystems having a high opacity has always been a great concern to papermanufacturers and paint manufacturers.

The degree of opacity of a particular substrate is the result of diffuselight-scattering which occurs when visible radiation is reflected fromparticles on the surface of the substrate and in the substrate mediumitself. It has been conventional to employ coatings of high densityinorganic fillers, such as titanium dioxide, calcium carbonate andcertain clays, to enhance the opacity of various substrates. However,the employment of such fillers has many disadvantages in the productionof paper, for example.

Generally, the use of such inorganic opacifying materials greatlyincreases the weight of the paper. This increase in weight is notconsistent with the increasing market demands for producing alighter-weight paper having high opacity.

Also, the incorporation of large amounts of fillers in paper results ina substantial loss of the paper web strength. In addition, the generallylow retention of the inorganic opacifiers in the paper results in asubstantial monetary loss by virtue of the high by-product wastematerial thereby resulting. More importantly, this results in heavycontamination of streams and other waterways. In addition to theforegoing disadvantages in the employment of such inorganic fillermaterials in paper. most inorganic fillers possess a lowopacity-to-weight ratio when incorporated in paper and other thinsubstrates.

It is therefore, an object of this invention to provide a means forincreasing the opacity of fibrous and nonfibrous substrates withoutsignificantly increasing the weight of said substrates, and at the sametime avoiding all of the aforementioned disadvantages of the inorganicopacifying materials.

It is another object of this invention to substantially improve theoptical properties, e.g., opacity and brightness, of fibrous substrateswithout decreasing the web strength of such substrate.

Another object of the present invention is to provide fibrous andnon-fibrous substrates having an increased opacity and brightnesswithout a substantial attendant increase in weight.

Still another object of the present invention is to provide opacifierswhich possess a high opacity-to-weight ratio when incorporated intocoatings on fibrous and in non-fibrous substrates.

Still another object of the present invention is to provide a method forthe production of the light weight opacifiers possessing a highopacity-to-weight ratio.

SUMMARY OF THE INVENTION These and other objects and features of thepresent invention are achieved by providing air-containing microcapsuleshaving an average particle size below about one micron, whichmicrocapsules when incorporated into coatings, on fibrous substrates andinto non-fibrous substrates greatly increase the opacity of suchsubstrates without substantially increasing the weight thereof.

For about the last ten years, microcapsules containing both liquid andsolid nucleus materials have found acceptance in a variety of commercialapplications. For example, one of the most widespread uses ofmicrocapsules have been in the art of transfer-copy systems. Otherrecent applications in which the microcapsules have been usedextensively are in adhesives and adhesive tapes, fertilizers,pharmaceuticals, foods and cosmetics.

It has now been found that microcapsular opacifiers may be producedwhich contain an encapsulated medium or core material which consistsessentially of air. Surprisingly, when the present air-containingmicrocapsules are coated onto and/or incorporated into a substrate, suchas paper, glass, film, metal, wood, etc., or incorporated into surfacefinishes such as paints, they significantly increase the opacity of thesubstrate by scattering back substantial amounts of the incident lightwhich would otherwise be transmitted by the substrate. Furthermore, ithas been found that when air-containing microcapsules having an averagediameter of less than about one micron, e.g., between about 0.1 andabout 1.0 micron, preferably between about 0.25 and 0.8 micron, areincorporated into and onto various substrates, high opacities resultwhich were heretofore unobtainable with similar amounts of inorganicopacifiers. Since the present aircontaining microcapsules are relativelylight in weight, the incorporation of such microcapsules into a fibrouscellulosic substrate, for example, will induce a high opacity for thesubstrate without greatly increasing the weight of said substrate. Also,the opacifiers of the present invention provide many advantages overthose conventionally employed, e.g., inorganic oxides. If desired, thepresent opacifiers may be employed in combination with such inorganicopacifiers as titanium dioxide and the like to enhance the opacifyingefiiciency.

The microcapsular opacifiers of the present invention comprise discrete,essentially spherical, air-containing microcapsules having substantiallycontinuous, solid walls and have an average particle diameter belowabout one micron.

The term substantially continuous solid walls as employed herein isintended to include solid-walled microcapsules which are stillsufiiciently porous to permit the escape of a core material in gaseousform therethrough upon the application of heat. The core material passesthrough the micropores of the capsule and is replaced therein with air.The core materials that may be employed in the production of the presentair-containing microcapsules are more particularly defined hereinafter.

The air-containing microcapsular opacifiers of the present invention maybe produced by a method which comprises providing discrete, essentiallyspherical precursor microcapsules having substantially continuous walls,said microcapsules having an average particle diameter of below aboutone micron and containing a core material, such as a water-immiscibleoily material selected from the group consisting of liquid and lowmelting oils, fats, and waxes, or a water-miscible liquid, such as, lowmolecular weight alcohols, ketones, etc., and heating the microcapsulesto a temperature sufficient to substantially complete ly drive-off thewater-immiscible oily core material from the microcapsules.

The precursor microcapsules of the present invention may be provided inany suitable manner, so long as the walls of the capsules havesufficient structural integrity to permit the core material to passtherethrough when heated without being ruptured or deformed into asubstantially non-spherical shape. According to one aspect of thepresent invention, precursor microcapsules are provided that have solidwalls of a hydrophobic resin and contain minute droplets of anoil-in-water emulsion.

According to another aspect of the present invention, solid-walled,precursor microcapsules containing a waterimmiscible oily material maybe provided by adding a cross-linking or complexing agent to a colloidalsolution of one or more emulsifying agents, wherein the emulsifyingagents possess groups capable of reacting with a crosslinking orcomplexing agent.

In the past, the production of microcapsules has involved, to a largeextent, a phenomenon referred to as coacervation. Coacervation is theterm applied to the ability of a number of aqueous solutions of colloidsto separate into two liquid layers, one rich in colloid solute and theother poor in colloid solute. Factors which influence this liquid-liquidphase separation are: (a) the colloid concentration, (b) the solvent ofthe system, (c) the temperature, (d) the addition of anotherpolyelectrolyte, and (e) the addition of a simple electrolyte to thesolution.

A unique property of coacervation systems is the fact that the solventcomponents of the two phases are the same chemical species. This is amajor distinguishing characteristic of coacervates as compared to twophase systems involving two immiscible liquids. Thus, a colloidal soluteparticle migrating across the interface of a two-phase coacervate systemfinds itself in essentially the same environment on either side of theinterface. From the viewpoint of composition, the difference between thetwo phases is a difference in concentration of solute species.structurally, the two phases differ in that the colloidal solute of thecolloid-poor phase is randomly oriented and the colloidal solute of thecoacervate or colloid-rich phase shows a great deal of order. In allcases where coacervation has been observed, the solute species aregeometrically anisotropic particles.

Coacervation can be of two general types. The first is called simple orsalt coacervation where liquid phase separation occurs by the additionof a simple electrolyte to a colloidal solution. The second is termedcomplex coacervation where phase separation occurs by the addition of asecond colloidal species to a first colloidal solution, the particles ofthe two dispersed colloids being oppositely charged. Generally,materials capable of exhibiting an electric charge in solution (i.e.materials which possess an ionizable group) are coacervatable. Suchmaterials include natural and synthetic macromolecular species such asgelatin, acacia, tragacanth, styrene-maleic anhydride copolymers, methylvinyl ether-maleic anhydride copolymers, polymethacrylic acid, and thelike.

With both simple and complex coacervate systems, a necessaryprecondition for coacervation is the reduction of the charge density ofthe colloidal species. In the case of simple coacervation, thisreduction of the charge density along with partial desolvation of thecolloidal species is similar to that preceding the flocculation orprecipitation of a colloid with the addition of a simple electrolytesince it is known that the addition of more electrolyte to a simplecoacervate leads to a shrinking of the colloid-rich layer and thesubsequent precipitation of the colloidal species. This same reductionof charge density along with partial desolvation of the colloidalspecies which precedes the precipitation of two oppositely chargedcolloids from solution may also be regarded to be the cause for thephase separation in a complex coacervate system. However, while thereduction of the charge density is a neces sary precondition forcoacervation, it is oftentimes not sufficient for coacervation. In otherwords, the reduction of the charge density on the colloidal particlesmust alter or modify the solutes0lute interactions to such an extentthat the colloidal particles will tend to aggregate and form a distinct,continuous liquid phase rather than a fiocculant or a solid phase. Thistendency is attributable to both coulombic and long-range Van der Waalsinteractions of large aggregates in solution. Thus, in both simple andcomplex coacervation, two-solution phase formation begins with thecolloidal species aggregating to form submicroscopic clusters; theseclusters coalesce to form microscopic droplets. Further coalescenseproduces macrosopic droplets which tend to separate into a continuousphase. This phase appears as a top or bottom layer depending upon therelative density of the two layers.

If, prior to the initiation of coacervation, a water-immisciblematerial, such as an oil, is dispersed as minute droplets in an aqueoussolution or sol of an encapsulating colloidal material, and then, asimple electrolyte, such as sodium sulfate, or another, oppositelycharged colloidal species is added to induce coacervation, theencapsulating colloidal material forms around each oil droplet, thusinvesting each of said droplets in a liquid coating of the coacervatedcolloid. The liquid coatings which surround the oil droplets mustthereafter be hardened to produce solid-walled microcapsules.

Coacervation encapsulation techniques require critical control over theconcentrations of the colloidal material and the coacervation initiator.That is, coacervation will occur only within a limited range of pH,colloid concentration and/or electrolyte concentration. For example, insimple coacervation, if a deficiency of the electrolyte is added,two-phase formation will not occur whereas, if an excess is added, thecolloid will precipitate as a lumpy mass. With complex coacervationsystems using a colloid having an iso-electric point, pH is especiallyimportant since the pH must be adjusted and maintained at a point whereboth colloids have opposite charges. In addition, when a gelablecolloid, such as gelatin, is used as the encapsulating material,coacervation must take place at a temperature above the gel point of thecolloid.

Accordingly, it is preferred to provide precursor microcapsules in theproduction of the air-containing opacifiers of the present invention, bya process which is devoid of the coacervation phenomenon and thedifficulties inherent therewith. The preferred processes for providingthe precursor microcapsules do not require strict control of the pH ofthe system, the electrical charge on a colloidal species to permitformation of microcapsules, a particular electrolytic concentration or acoacervating agent. However, precursor oil-containing microcapsulesproduced by the technique known as coacervation can be employed for theproduction of the opacifiers of the present invention, if desired.Additionally, any microencapsulation method, whether chemical orphysical, that is capable of yielding air-containing microcapsuleshaving an average diameter below about one micron may be employed.

According to one aspect of the present invention, precursormicrocapsules are provided which have solid walls of a hydrophobic resinand contain minute droplets of an oil-in-water emulsion. The process forproviding such microcapsules may be described briefly as a simpleadmixing of at least four ingredients. These ingredients are:

(A) a water-immiscible oily material selected from the group consistingof liquid and low melting oils, fats, and waxes;

(B) an amphiphilic emulsifying agent;

(C) at least one solution comprising a polymeric resin,

said solution selected from the group consisting of;

(1) solutions comprising a hydrophobic, thermoplastic resin as thesolute, said resin not having appreciable solubility in the oilymaterial, and a waterand oil-miscible organic liquid as the solvent,said thermoplastic resin being capable of being separated in solidparticle form from solution upon dilution with water,

(2) solutions comprising a partially condensed thermosetting resin asthe solute and water as the solvent, said resin condensate being capableof being separated in solid particle form from solution upon dilutionwith water, and

(3) mixtures of (1) and (2); and,

(D) water in a quantity sufficient to cause the separation of at leastone of said polymeric resins from so-' lution.

The sequence of said admixing must be such that encap sulation of theemulsion by at least one of the synthetic resins in the admixture bydilution and ultimate separation from solution in solid particle formabout a nucleus of oil in water upon dilution with Water occurs nosooner than simultaneously with the formation of the emulsion. In otherwords, dilution, which can be performed by the addition of water to theoil-emulsifier-resin solution admixture or by the addition of the resinsolution to the water-oil-emulsifier admixture, must be the finaloperation of the process. Thus, in the first case, the emulsifyingoperation and the encapsulation operation can be considered to takeplace simultaneously, whereas, in the second case, the emulsion isalready formed when it is admixed with the resin solution.

As previously mentioned, the core material, e.g., a water-immiscibleoily material, in the precursor microcapsules is driven from themicrocapsules and is replaced by air. By water-immiscible oilymaterials, as employed herein, is meant lipophilic materials which arepreferably liquid, such as oils, which will not mix with Water and whichcan be driven through the porous, solid walls of the particularprecursor microcapsules employed. The discrete microcapsules of thepresent invention may be provided with low melting fats and waxes as thelipophilic material. However, oils are the preferred core material,since they do not require special temperature maintenance during theproduction of the microcapsules. Furthermore, oils are more easilyvolatilized and driven through the micropores of the walls of themicrocapsules by the application of heat.

In general, the lipophilic nucleus materials may be natural or syntheticoils, fats, and waxes or any combination thereof which can be removedfrom the microcapsules at the desired temperatures. Among the materialsthat can be employed in the process of the present invention are:mineral spirits, natural oils, such as castor oil, soyabean oil,petroleum lubricating oils, fish liver oils, and essential oils, such asmethyl salicylate and halogenated biphenyls; low melting fats and Waxes.

The preferred lipophilic material for employment in the presentinvention are those oils having a fairly high vapor pressure (highvolatility), so that it can be completely and easily expelled throughthe micropores of the solid-walled microcapsules by the application ofmoderate amounts of heat. It is especially preferred to employ oilswhich can be driven from the microcapsules at temperaturesconventionally employed in the drying of paper webs or paper coatings,e.g., about 85 C. Preferred oils for use in the present inventioninclude mineral spirits,

chlorinated biphenyls, toluene, styrene, turpentine, and oils having alike volatility.

The emulsifying agents which may be used in the formation of themicrocapsules are amphiphilic. That is, while the emulsifiers aregenerally preferentially soluble in one phase of the emulsion, they dopossess an appreciable aflinity for the other phase. It can be said,then, that an amphiphilic emulsifier gives oil a more hydrophilic naturethan it had before, and, conversely, gives water a more lipophilicnature. Exemplary of the amphiphilic emulsifying agents which can beused in the instant invention are: naturally-occurring, lypophiliccolloids including gums, proteins and polysaccharides, such as, gumarabic, gum tragacanth, agar, gelatin and starch; and syntheticmaterials such as, hydroxyethyl cellulose, methyl cellulose, polyvinylpyrrolidone, and copolymers of methyl vinyl ether and maleic anhydride.

The thermoplastic resins which may function as the encapsulatingmaterials must be of a hydrophobic nature. In other words, they shouldnot be capable of dissolving readily in water. While it is true that allresins exhibit some, even though very small hydrophilic properties,those resins acceptable for use in this aspect of the invention must forthe most part be hydrophobic, that is, more lipophilic than hydrophilic.

In general, the thermoplastic resins are to be macromolecular polymers,copolymers, block polymers, and the like. The preferred resins are thosecontaining nonionizable groups, since the extent to which a resinionizes has an ultimate effect on the resins hydrophilic-hydrophobicproperties. Resins such as polyvinyl chloride and polystyrene arenon-ionizable and are, therefore, preferred. However, other resins whichcan be used are polyvinyl acetate, vinyl chloride-vinylidene chloridecopolymers, cellulose acetate and ethyl cellulose. Novolak resins whichare linear, thermoplastic condensation products of phenol andformaldehyde, are also capable of being used in the present invention asthe thermoplastic resin. The novolaks are permanently fusible andsoluble as long as their molecular structure is linear.

The selection of solvents for the resin to be used will depend on thespecific encapsulating thermoplastic resin and the oil employed.Furthermore, the solvent must be sufficiently miscible with water inorder for the resin to be separated from its solution when the oil-resinmixture is admixed with water.

In general, the solvents which are preferable are organic and of lowpolarity. Tetrahydrofuran has been used successfully with all of theresins heretofore mentioned and is, therefore, preferred. Examples ofother solvents which are suitable include dioxane, cyclohexanone, methyltetrahydrofuran, methyl isobutyl ketone and acetone.

A small amount of stabilizer may be incorporated with the solution ofthe thermoplastic resin to increase the resins stability towards heat,light and atmospheric oxygen. Examples of stabilizers which may be usedinclude dibasic lead phosphite, dibasic lead stearate, tribasic leadsulfate monohydrate, dibutyltin maleate and others well known to theart. The use of such stabilizers is wholly conventional.

The partially condensed thermosetting resins which may be used invarious embodiments of this invention must also be of a hydrophobicnature in their solid, infusible state. These resins comprise that broadclass of compositions defined as formaldehyde condensation products andinclude condensation reaction products of formaldehyde with phenols,such as, hydroxybenzene (phenol), m-cresol and 3,5-xylenol; carbamides,such as, urea; triazines, such as, melamine; amino and amido compounds,such as, aniline, p-toluenesulfonamide, ethyleneurea and guanidine;ketones, such as, acetone and cyclohexanone; aromatic hydrocarbons, suchas, naphthalene; and heterocyclic compounds, such as, thiophene. Underthe influence of heat, these resins change irreversibly from a fusibleand/or soluble material into an infusible and insoluble material.

The preferred formaldehyde condensation products employed in thisinvention are partially-condensed melamineformaldehyde,phenol-formaldehyde and urea-formaldehyde resins. These partiallycondensed resins can be prepared easily according to conventionalpractices. For example, a melamine-formaldehyde partial condensate orsyrup, which was used in a number of the examples enumerated below, isprepared by refluxing 125 grams of melamine in 184 milliliters offormalin (37% by weight formaldehyde) neutralized to a pH of 8 withsodium carbonate. The mole ratio of formaldehyde to melamine in thisreaction mixture is 2.3 to l. The reaction continues for about 1 to 1 /2hours at a temperature between 92 and 96 C. or until 1 volume of thecondensate becomes turbid when diluted with 2 to volumes of water. Thecondensate can be used immediately or can be stored for later use byadding a small amount, about 6 to by weight, of methanol to thecondensate. The methanol prevents any further rapid condensation of theresin solution upon standing and can be evaporated from the syrup eitherprior to or during the admixing operation. The resinous condensate orsyrup, either with or Without methanol, defines an aqueous solution of apartially-condensed, highly cross-linkable resin, said solution beingcapable of being diluted up to at least twice its volume before anyappreciable separation of the resin from its solution occurs. Afterseparation of the resin from its solution, the condensation reactioncontinues with time to effect additional cross-linking of the partiallycondensed materials. This additional condensation or cross-linking maybe accelerated by the application of heat to the precipitated particles.Thus, microcapsules comprising walls of a thermosetting resin materialbecome harder with the passage of time.

Preferably, a small amount of a stabilizer is added to the thermosettingresin syrup in order to improve the stability of the resins towardsheat, light and oxygen. For example, from about 0.3 to 0.5% by weight ofa conventional stabilizer such as zinc stearate or dibasic lead stearatemay be used.

The dilution of either one or both of the resin solutions should takeplace as the final operation of the process, which dilution takes placeslowly and under conditions of brisk agitation. In other words, thesequence of admixing the ingredients may generally proceed in any orderso long as the separation or precipitation of a resin from solutionresults in the encapsulation of emulsion droplets. Thus, when a singleresin is to be used, the order of additions must be such that eitherwater or the resin solution is the last addition. Microcapsules may bepro- I vided which contain a dispersion comprising one or moreemulsion-containing microcapsules. Thus, once an oil-inwater emulsion isencapsulated, a second dilution operation may be effected by simplyadding another resin solution to the aqueous dispersion of thefirst-formed microcapsules. Consequently, microcapsules containingmicrocapsules are produced.

Brisk agitation is required in order to obtain very small droplets ofthe emulsion, and, ultimately, very small capsules. Thus, microcapsuleshaving diameters ranging from below about one micron and preferablybetween about 0.25 and about 0.8 micron may be produced according to thepractices of this invention. Agitation may be achieved by means of ahigh speed mixer or impeller, by ultrasonic Waves or by otherconventional means. Brisk agitation need be maintained only in the zoneof admixing and not throughout the entire volume of the liquid to whichthe outer liquid is being added. Agitation should be conducted in amanner such that the emulsion droplets have an average diameter betweenabout 0.25 and about 0.5 micron prior to encapsulation, so that uponcompletion of encapsulation the average final particle diameter does notexceed 0.8 to about 1.0 micron.

The slower the speed of admixing, the more impermeable the capsule wallswill be to both internal and ex- 8 ternal leakage. Slow admixture may beachieved by any of the conventional means, such as by spraying in theform of a fine mist or by dripping.

Regardless of the manner of providing the oil-containing precursormicrocapsules employed, the microcapsules are heated to temperatureswhich cause the oily material to volatilize and pass through themicropores in the solid walls of the microcapsules. The heating of themicrocapsules may take place at any time subsequent to their formation.In the case of microcapsular opacifiers to be used on fibroussubstrates, the oily material may be driven from the microcapsuleseither before or subsequent to their being coated onto the substrate.For example, a dispersion of the oil-containing microcapsules may bespray-dried so as to provide air-containing microcapsules, which may bethen coated onto the substrate.

As previously mentioned, the precursor microcapsules may contain awater-miscible core material. For example, if the oily material isdriven from the suspended microcapsules prior to their being coated ontoor incorporated into a substrate or a surface finish, the oily materialmay be replaced by another liquid such as water or whatever other liquidmay constitute the medium in which the microcapsules are suspended.Likewise, a dispersion of the microcapsules having a water-miscible corematerial may be spray-dried to provide the air-containing microcapsulesof the present invention.

FIG. 1 illustrates the various alternative modes of producing a webmaterial coated with the air-containing microcapsules of the presentinvention.

In the encapsulating process shown in FIG. 1, the core is exemplified byan oily material, such as a chlorinated biphenyl which is admixed withan aqueous solution of an emulsifying agent, e.g., methyl cellulose, andagitation is continued until emulsion droplets having an averagediameter less than one micron are produced. Next, an aqueous solution ofan encapsulating agent, e.g., urea formaldehyde is added to the emulsionwith brisk agitation and solid-walled microcapsules are immediatelyformed. The microcapsules may be optionally cured, e.g., by the additionof glyoxal, and then any one of four procedures may be followed. Thus,the microcapsular dispersion may be heated to a temperature of, forexample, between about and about C. to drive off the oily materialthrough the micropores of the capsule walls and then the air-containingmicrocapsules may be coated onto the web and dried. Any suitabletemperatures may be employed to drive the oily material from themicrocapsules, so long as the microcapsules are not destroyed.

Alternatively, the microcapsules may be heated while in dispersion todrive off the oil and subsequently cellulose fibers may be added to thedispersion. The resulting admixture of the air-containing opacifiers andfibers may be formed into a web and dried.

Still another alternative is to coat the oil-containing microcapsulesonto a fibrous web and then beat the microcapsules to drive the oiltherefrom.

In the case of surface finishes, such as paints, the core material maybe driven from the microcapsules either prior or subsequent to theirincorporation into the paint as opacifiers.

FIG. 2 shows a process by which an oil-in-water emulsion is encapsulatedby a thermoplastic resin. The resin, in the form of a solution, isadmixed slowly with the emulsion. However, the admixture may involve theaddition of the emulsion to the resin solution. In either case, thethermoplastic resin separates from its original solution as minute,solid-walled particles by reason of the dilution of the resin solutionby the water of the emulsion. Each of the solid-walled particles maycontain one or more oilin-water emulsion droplets. It should be notedthat the resin should not have appreciable solubility in the corematerial.

On completion of the dilution operation, the admixture constitutes theminute resin particles (each containing droplets of the emulsion) evenlydispersed in an aqueous medium comprising water, the solvent for theresin and residual emulsifying agent. Essentially all of the oilymaterial (in emulsion form) is contained within the resin particles. Thethus-formed microcapsular dispersion may be heated to drive off the oilor may be coated directly onto a web material and heated to produce acoating of opacifiers. As an optional step, a small amount of a bindermaterial may be added to the microcapsular dispersion prior to coating.Such additional aids in binding the microcapsules to the web material.

FIGS. 3 and 4 show two alternative processes of the microencapsulationof an oil-in-water emulsion with a thermosetting resin. In FIG. 3, theprocess shown is substantially the same as that shown in FIG. 2 with theexception that a partially condensed, aqueous, thermosetting resin syrupis substituted for the thermoplastic resin solution. Although not shownin FIG. 3, the optional step of adding a binder material to themicrocapsular dispersion prior to coating may be performed.

The process as shown in FIG. 4 involves first preparing a water-in-oilemulsion by admixing the oily material with an amphiphilic emulsifyingagent and the thermosetting resin syrup. By slowly admixing water withthis emulsion, the emulsion will gradually invert to an oil-in-wateremulsion. The dilution of the initial emulsion with water simultaneouslyinduces the precipitation of the thermosetting resin, therebyencapsulating the oil-in-water emulsion within the precipitated resinparticles. The resulting microcapsules, which are evenly dispersedthroughout an aqueous medium containing residual emulsifying agent, maythen be coated onto a web material and dried to drive off the oil, or,alternatively, an additional amount of a binder may be admixed with thedispersion prior to coating, such as shown in FIG. 2.

FIGS. 5, 6, and 7 illustrate three alternative processes for themicroencapsulation of an oil-in-water emulsion involving both athermoplastic and a thermosetting resin. In FIG. 5, a process is shownwhich may be considered a modification of the process shown in FIG. 4.More specifically, the sequence of admixing in the FIG. 5 process isidentical to that of FIG. 4, except that a solution of a thermoplasticresin in a waterand oil-miscible solvent is added to the initialemulsion prior to dilution with water. On subsequent dilution theemulsion inverts and the resins precipitate to encapsulate the emulsiondroplets.

Both FIGS. 6 and 7 show the encapsulation of microcapsules wherein theinitial microencapsulation of the oil-in-water emulsions takes the formof the processes shown in FIGS. 4 and 2, respectively. Thus, in theprocess of FIG. 6, a thermoplastic resin solution is admixed with theaqueous dispersion of thermosetting resin microcapsules producedaccording to the process of FIG. 4. The water which is present in thedispersion effects a dilution of the thermoplastic resin solution, whichdilution induces the precipitation of the thermoplastic resin.Essentially all of the previously formed thermosetting resinmicrocapsules are, thereby, encapsulated by the newly precipitatedthermoplastic resin. In addition, some of the residual emulsifying agentin the dispersion medium is caused to be entrapped within thethermoplastic resin microcapsules.

Similarly, in the process of FIG. 7, a partially condensed, aqueous,thermosetting resin syrup is admixed with the aqueous dispersion ofthermoplastic resin microcapsules produced according to the process ofFIG. 2. The water in the dispersion causes the precipitation of thethermosetting resin, thus, encapsulating the dispersed, thermoplasticresin microcapsules.

The substrate employed in the present invention may be either a fibroussubstrate, such as paper, a non-fibrous substrate, such as a film or asurface finish, such as paint. However, the microcapsules, such as thoseproduced by the herein disclosed proceses are also capable of being 10coated onto other fibrous substrates, such as plastic and fabric ortextile webs.

Generally, there is sufiicient residual emulsifying agent remaining inthe microcapsular dispersion after separation of the resin andencapsulation of the emulsion that no additional binding agent need beused if the capsules are to be applied to a fibrous substrate. Materialssuch as gelatin and gum arabic have been used conventionally as bindingagents. However, it is preferable to add an additional binder such ashydroxyethyl cellulose, methyl cellulose or starch to the system.

According to another aspect of the present invention, the oil-containingprecursor microcapsules are preferably provided by a process whichincludes forming a primary oil-in-water emulsion, which emulsioncomprises the water-immiscible oily material previously described. Theoily material is dispersed in the form of microscopic droplets in acolloidal solution of one or more emulsifying agents. At least one ofthe said emulsifying agents must possess groups capable of reacting witha cross-linking or complexing agent to form a capsule wall around saiddispersed microscopic droplet. The cross-linking or complexing agent isslowly added to the emulsion with brisk agitation, and this is continueduntil the final microcapsules are formed having substantially continuoussolid walls, as hereinabove defined. The emulsion containing theprecursor microcapsules may be heated to produce the opacifiers or maybe directly coated onto a web material as previously described.Alternatively, the microcapsules may be separated from the emulsion byphysical means, such as filtration, centrifugation, or spray drying.Subsequently, the microcapsules may be redispersed in a solution of abinder and coated onto a web material or may be dispersed in anon-fibrous substrate.

The encapsulating material of this aspect may also be an emulsifyingagent which is self-complexing or selfcross-linking. In such a case theaddition of a different cross-linking or complexing agent isunnecessary. Exemplary of emulsifying agents having the aforesaidcharacteristics which permit their employment are: naturallyoccurringcolloids including gums, proteins and polysaccharides, such as gumtragacanth, guar gums and gelatin; and synthetic materials such aspolyvinyl alcohol and copolymers of methyl vinyl ether and maleicanhydride. Suitable copolymers of methyl vinyl ether and maleicanhydride are commercially available from the General Aniline and FilmCorporation and are sold under the trademark Gantrez. Thesewater-soluble copolymers have the general structure OCHa The above listcomprises both gellable and non-gellable emulsifying agents, e.g.gelatin and polyvinyl alcohol. Emulsifying agents which are selfcross-linking or selfcomplexing include certain derivatives of guar gum,such as those which are commercially available from Stein, Hall andCompany sold under the trademark Jaguar. These materials are naturalhydrophilic colloids that are produced by the extraction of guar gumfrom the endosperm portion of eyamopsis tetragonalobus seeds and arecomprised of a straight chain galacto mannan polysaccharide made of manymanose and galactose units linked together.

The cross-linking or complexing agents employed with the aforesaidemulsifying agents are selected from three broad categories: 1)monomeric organic compounds, such as the aldehydes, e.g. formaldehyde,glyoxal and other formaldehyde donors, trioxane ethanolamine, andethylene diamine; (2) ordinary inorganic compounds, such as sodiumborate and boric acid; and (3) macromolecular splecies, such as gelatin,gum tragacanth, and methylcelu ose.

While some of the cross-linking or complexing agents are suitable foruse with a plurality of emulsifying agents, others are not. Thus, thepreferred cross-linking or complexing agent-emulsifying agent pairsinclude: (1) gelatin with an aldehyde, such as formaldehyde; (2)polyvinyl alcohol with sodium borate; (3) copolymers of methyl vinylether and maleic anhydride with any one of gelatin, gum tragacanth,ethanolamine, ethylene diamine, polyvinyl alcohol; (4) guar gumderivatives with any one of sodium borate or methylcellulose; and (5)self-complexing guar gum derivatives with themselves.

The cross-linking or complexing agent is utilized in amounts sufiicientto result in the formation of microcapsules. The relative amounts varywith the particular system, and may be easily determined in each case.

FIGS. 8 and 9 of the attached drawings illustrate processes for theprovision of microcapsules according to the second aspect of theinvention. In the process shown in the flow sheet of FIG. 8, a primaryoil-in-water emulsion is prepared by dissolving the emulsifying agent orcombination of agents in the oily material and subsequently adding waterto emulsify.

The water may be added to the emulsifying agent-oil mixture eitherquickly or slowly with agitation. If the water is added slowly to theoil phase containing the emulsifying agent or agents, a water-in-oilemulsion is formed, which eventually is inverted to an oil-in-wateremulsion with the further addition of water. Such an inversion stepresults in a more stable emulsion with some systems, e.g., a methylcellulose-guar gum derivative system.

The temperature of emulsification may be varied over a broad range.However, the temperature must be kept above the gelling point of theemulsifying agent or agents only if a gellable emulsifying agent isused. Therefore, when a non-gellable emulsifying agent is used, e.g.,polyvinyl alcohol, the temperature during emulsification can be variedappreciably without altering the final desired results.

Subsequent to the emulsification process, the cross-linking orcomplexing agent is added to the oil-in-water emulsion, slowly, and withbrisk agitation to form the precursor microcapsules. Agitation may beachieved by means of a high speed mixer or impeller, by ultrasonic wavesor by other conventional means so long as microcapsules having aparticle size below one micron are formed.

If the emulsifying agent is of the self-complexing variety, e.g., aself-complexing guar gum derivative, the crosslinking or complexingagent comprises the same material as the emulsifying agent.

Alternatively, the emulsion containing the microcapsules may be eithercoated directly onto a web material and dried or the microcapsules maybe separated from the emulsion by some physical means such asfiltration, spray drying centrifugation; redispersed in a solution of abinder; coated onto a web material and dried. Removal of the oil fromthe interior of the capsule may be done either before or after coating,as before. Suitable binders include methyl cellulose, starch, casein,polyvinyl alcohol, synthetic latex, and styrene-butadiene rubber.Alternatively, materials such as urea-formaldehyde ormelamineformaldehyde condensates may be employed.

In the encapsulation process illustrated in FIG. 9, the oil-in-wateremulsion is prepared by dissolving the emulsifying agent (or agents) inwater and subsequently adding the oily material to the water solutionwith agitation until complete emulsification has occurred. The emulsionmay then be diluted with water to give the desired viscosity suitablefor coating. Capsule diameters suitable for producing the microcapsularopacifiers of the present invention, i.e., in the range below onemicron, are likewise obtainable by the process of FIG. 8 by addingcross-linking or complexing agents with agitaation as previouslydescribed.

FIG. 10 represents a cross-sectional view of a portion of a fibroussubstrate produced according to the practices of the present inventionwherein a paper web material 10 contains a substantially uniform coatingof opacifiers 12 having an average diameter below about one micqon andcontaining air as the core material. The binding agent employed tosecure the opacifiers to the paper web is not shown.

The production of the precursor microcapsule as hereinabove described isdisclosed in copending applications Ser. Nos. 503,391, filed on Oct. 23,1965, now US. Patent No. 3,418,656, and 583,046, filed Sept. 23, 1966,the disclosures of which are hereby incorporated by reference.

The following examples illustrate the production of aircontainingmicrocapsular opacifiers and constitute the best modes contemplated forcarrying out the present invention. The ream of paper as employed in thefollowing examples and claim comprises 500 sheets of 25 inch by 38 inchpaper or a total of 3300 square feet of paper. Likewise, the paperemployed in the following examples is bond paper (32.5 pounds per ream)having a TAPPI opacity of 69 percent points prior to coating.

Example 1 On hundred grams of styrene (monomer) are emulsified with 370grams of a 7.5 percent by weight methyl cellulose (25 centipoises)solution in water in a Waring Blendor. Emulsification is continued untilthe average particule diameter of the emulsion droplets is about 0.5micron. Subsequently, 20 grams of an aqueous B-stage ureaformaldehydecondensate by weight solids) are slowly added to the emulsion withcontinued agitation in order to induce encapsulation.

The oil-containing microcapsules are coated onto a web comprising bondpaper. The bond paper is coated with 11.5 pounds per ream of theoil-containing precursor microcapsules. The paper web is dried at atemperature of about C., for a period of time sufiicient to remove thestyrene monomer and result in the air-containing microcapsules. Thesemicrocapsules have an unexpectedly high TAPPI opacity of 86.5 percentpoints, while at the same time the weight of the paper web is onlyincreased to the extent of 3.6 pounds per ream of paper.

Example 2 The method of Example 1 is repeated employing grams of achlorinated biphenyl oil (Aroclor 1221) instead of styrene and thismaterial is emulsified with 720 grams of a 4 percent by weight gelatinsolution under conditions of brisk agitation. The microcapsules have thesame diameter as the previous example. To avoid gelation, theemulsification is performed at a temperature of 60 C.

The oil-containing microcapsules are coated onto the bond paper of theprevious example and are dried at a temperature of 85 C. A resultingcoat weight of 4.5 pounds per ream of air-containing microcapsules onthe bond paper is thereby provided. The air-containing microcapsulesproduce a final TAPPI opacity of 89.6 percent points, which constitutesa 20.6 percent points increase over the initial TAPPI opacity of theuncoated bond paper, viz, 69 percent points.

Example 3 The emulsion procedure of Example 2 is repeated, with theexception that 200 grams of a 15 percent by Weight gum arabic solutionis employed at room temperature in place of the gelatin solution.

A coat weight of 6.8 pounds of the air-containing microcapsules per reamof the bond paper results in a final TAPPI opacity of 92 percent. Thisconstitutes an increase of 23 percent points TAPPI opacity over that ofthe original paper.

Example 4 The procedure of Example 3 is repeated utilizing 365.8 gramsof an 8.5 percent solution of methyl cellulose (15 centipoisesviscosity) as the emulsifying agent in place of gum arabic. Themicrocapsules containing the chlorinated biphenyl oil have an averagediameter below one micron and are coated onto the bond paper as beforeand are dried at a temperature of about 85 C., which is sufiicient todrive off the chlorinated biphenyl. The resulting coat weight of theair-containing microcapsules is 2.3 pounds of microcapsules per ream ofthe paper. A measurement of the TAPPI opacity of the coated paperindicates an increase of 13.6 percent points in TAPPI opacity over theoriginal paper for a value of 82.6 percent points.

Examples -11 For comparative purposes, the bond paper employed in theprevious examples is coated with titanium dioxide in various coatweights. The resulting TAPPI opacity is then measured for eachrespective weight.

As seen from the foregoing comparative examples, a substantially highercoat-weight of the inorganic pigment, viz, titanium dioxide, is requiredto give the same opacities as the air-containing microcapsules. Forexample, a coat weight of 4.5 pounds of titanium dioxide per ream ofbond paper, as shown in Example 6, is required to give the 86.5 percentpoints TAPPI opacity that is achieved in Example 1 with the employmentof only 3.6 pounds per ream of the air-containing microcapsularopacifiers. Likewise, a coat weight of 8.4 pounds of the titaniumdioxide per ream of paper is required to give a TAPPI opacity of about92 percent points (see Example 9), while only 6.8 pounds per ream of theair-containing microcapsules resulted in a final TAPPI opacity of 92percent points (see Example 3, above).

Example 12 A primary oil-in-water emulsion is formed by adding 50milliliters of chlorinated biphenyl oil to ten grams of a purifiedgelatin which is dissolved in 100 grams of water at a temperature ofabout 50 C. over a period of 20 to 30 minutes. Subsequently, 100milliliters of 1 M formaldehyde solution in water are slowly added tothe emulsion with brisk agitation followed by the addition of 50milliliters of water. The addition of the formaldehyde results in theformation of well-defined microcapsules having a particle size of 1.0micron.

The microcapsules are then filtered, washed with successive 50milliliter portions of water, methanol and Formalin solution, andredispersed in 100 milliliters of water containing 4 grams of a bindingagent comprising methyl cellulose. The solution of methyl cellulosecontaining the microcapsules is coated onto a paper web and dried at 85C. to drive 01f the oil.

Example 13 One hundred grams of water containing 5 grams of methylcellulose are emulsified with 25 grams of chlorinated biphenyl. Tengrams of Gantrez39 (a copolymer of methyl vinyl ether and maleicanhydride) are added to the emulsion and emulsification is allowed toproceed for an additional to 15 minutes. Subsequently, 10 milliliters ofethylene diamine are slowly added with brisk agitation, resulting in theformation of Well-defined microcapsules having an average diameter of0.9 micron. The viscosity of the above emulsion, containing themicrocapsules is further regulated with additional water (between 50 and60 milliliters of water). Next, the dispersion is heated to 80 C. afterbeing coated onto a paper web in order to produce the opacifiers. Thecoated paper web is subsequently dried and has a highly opaque surface.

Example 14 An emulsion is prepared by adding 200 grams of mineralspirits (Phillips 66 Soltrol 130) in a Waring Blendor and emulsifying itwith 365 grams of an 8.2% by weight methylcellulose (15 cps.) solutionin water using brisk agitation. Emulsification is continued until theaverage diameter of the emulsion droplets is about 0.8 micron.Subsequently, 90 grams of a B-stage urea-formaldehyde (65 solids byweight solution in water) resin are added; this is followed by the slowaddition of 40 milliliters of a 15% by weight citric acid solution inwater. The microcapsules are then coated onto paper, and the coatedpaper is dried in an oven at C. for 15 minutes. The resulting coatweight (after the evolution of the mineral spirits from themicrocapsules) is 5.68 lbs. per ream and the coresponding increase inTAPPI opacity is 16.4% points.

Example 15 One hundred-fifty grams of mineral spirits are emulsifiedwith 365 grams of a 20% by weight polyvinyl alcohol (Du Ponts Elvanol52-22) solution in water. Emulsification is continued until the averagediameter of the emulsion droplets is about 1 micron. Subsequently, gramsof urea-formaldehyde solution are added. The microcapsules are coatedonto paper, and the coated paper is dried in an oven at 85 C. for 15minutes. The resulting coat weight (after the evolution of the mineralspirits from the microcapsules) is 4.0 lbs. per ream and thecorresponding increase in TAPPI opacity is 10% points.

Example 16 Mineral spirits in the amount of grams are emulsified with300 grams of a 13% by weight styrene-maleic anhydride solution in water.Emulsification is continued until the average diameter of the emulsiondroplets is about 1 micron. Subsequently, 90 grams of a B-stageurea-formaldehyde (65% solids by weight solution in water) resin areadded and the microcapsules coated onto paper. The coated paper is driedin an oven at 85 C. for 15 minutes. The resulting coat weight (after theevolution of the mineral spirits from the microcapsules) is 6.22 lbs.per ream and the corresponding increase in TAPPI opacity is 17.3%points.

Example 17 One hundred-fifty grams of xylene are emulsified with 365grams of 8.2% by weight methylcellulose solution in water.Emulsification is continued until the average diameter of the emulsiondroplets is about 1 micron. Subsequently, 60 grams of a B-stageurea-formaldehyde resin are added and the microcapsules coated ontopaper. The coated paper is dried in an oven at 85 C. for 15 minutes. Theresulting coat weight (after the evolution of the xylene from themicrocapsules) is 5.92 lbs. per ream and the corresponding increase inTAPPI opacity is 15% points.

Example 18 One hundred grams of a chlorinated biphenyl (Aroclor 1221)are emulsified with 365 grams of an 8.2% by weight methylcellulosesolution in water. Emulsification is continued until the averagediameter of the emulsion droplets is about 0.8 micron. Subsequently, 60grams of a B-stage melamine-formaldehyde resin is added and themicrocapsules are coated onto paper. The coated paper is dried in anoven 85 C. for 1 hour. The resulting coat weight (after the evolution ofthe chlorinated biphenyl from the microcapsules) is 5.16 lbs. per reamand the corresponding increase in TAPPI opacity was 15 points Example 19Seventy-five grams of mineral spirits are emulsified with 90 grams of a9.1% starch solution and 90 grams of an 8.2% by weight methylcelluosesolution in water. Emulsification is continued until the averagediameter of the emulsion droplets is about 0.7 micron. Subsequently, 45grams of a urea-formaldehyde resin is added and the microcapsules arecoated onto paper. The coated paper is dried in an oven at 85 C. for 15minutes. The resulting coat Weight (after the evolution of the mineralspirits from the microcapsules) is 5.2 lbs. per ream and thecorresponding increase in TAPPI opacity is 12% points.

Example A chlorinated biphenyl (Aroclor 1221) in the amount of 100 gramsare emulsified with 200 grams of a 15% gum arabic solution.Emulsification is continued until the average diameter of the emulsiondroplets is about 1.7 microns. Subsequently, 20 grams of a B-stageurea-formaldehyde resin and 5 grams of glyoxal are added and themicrocapsules are cured for 4 hours at 80 C. The microcapsules are thencoated onto paper, and the paper is dried in an oven at 80 C. for 1hour. The resulting coat weight (after the evolution of the chlorinatedbiphenyl from the microcapsules) is 4.9 lbs. per ream and thecorresponding increase in TAPPI opacity is 19% points.

Example 21 Sixty grams of low density (0.92) polyethylene are melted ina high shear heated mixer at 130 C., 40 grams of dry, air-filledmicrocapsules (of approximately 1 micron average diameter) are added tothe molten polyethylene and mixing is continued until a good dispersionis obtained. When a film of 5 mil thickness is compression molded at 325F. and 2,000 p.s.i. pressure, the TAPPI opacity of the resulting film is65% points. A similar polyethylene film of comparable thickness issubstantially transparent.

Example 22 Example 23 Seventy-five grams of mineral spirits areemulsified with 182.5 grams of an 8.2% (by weight) methylcellulosesolution in Water. Subsequently, 70 grams of a 40% (by weight) solutionof a phenoxy resin comprising the condensation product of bisphenol-Aand epichlorohydrin v (Union Carbides PKHH resin) in methyl ethyl ketoneare added slowly and with brisk agitation. Mixing is continued untilmicrocapsules having an average diameter of about 0.7 micron areobtained. The solution containing the microcapsules is coated onto paperand dried in an oven at 85 C. for 20 minutes to remove'the mineralspirits from the microcapsules. A coat weight of 3.84 lbs. per ream ofthe air-containing microcapsules result in an increase in the TAPPIopacity of the paper of 9% points.

Example 24 Using the British standard sheet mold, handsheets areprepared corresponding to a basis ream weight of 48 pounds per 3,300square feet from a furnish consisting of 75% bleached sulfate pulp frommixed southern hardwoods and 25% bleached southern pine sulfate pulp.Similar handsheets corresponding to the same final basis weight areprepared by adding approximately 10% (by weight of the fiber furnish) ofair-containing microcapsules. An increase of about 7 to 8 percent pointsin 16 opacity is obtained with the sheet containing the airmicrocapsules.

Example 25 Example 14 is exactly duplicated with the only differencebeing that prior to coating the air-containing microcapsules onto thepaper web; 6 grams of TiO are added to the capsule-containing solution.The resulting admixture is coated onto paper and dried in an oven at C.for 15 minutes. The resulting coat weight (after the evolution of themineral spirits from the microcapsules) is 5.0 lbs. per ream and thecorresponding increase in TAPPI opacity is 19.4% points.

The opacifiers of the present invention may be employed in all knownapplications where conventional pigments have been used for inducing orincreasing opacity. For example, the opacifiers may be used in paints,as inks, in plastics, on metals, glass, Wood, plaster, in films, onfabrics, paper and the like.

Although the invention has been described in considerable de't'ail withparticular reference to certain preferred embodiments thereof,variations and modifications can be effected within the spirit and scopeof the invention as described hereinbefore, and as defined in theappended claims.

What is claimed is:

1. A method for the production of air-containing microcapsularopacifiers, which method comprises providing discrete, essentiallyspherical precursor microcapsules having substantially continuous,organic, polymeric soli walls, said microcapsules having an averageparticle diameter of below about one micron and containing a liquid corematerial, and heating said microcapsules to a temperature suflicient tosubstantially completely drive off said core material from saidmicrocapsules and replace said core material with air, saidair-containing microcapsules being capable of increasing the TAPPIopacity of a ream of bond paper having a TAPPI opacity of 69 percentpoints without said air-containing microcapsules, by at least 9 percentpoints when said paper is provided with 3.84 pounds per ream of saidair-containing microcapsules.

2. The method of claim 1 wherein said liquid core material is awater-immiscible material.

3. The method of claim 2 wherein said water-immiscible material is anoily material selected from the group consisting of liquid and lowmelting oils, fats and Waxes.

4. The method of claim 3 wherein the water-immiscible oily material isselected from the group consisting of mineral spirits, chlorinatedbiphenyl, toluene, styrene and turpentine.

5. The method of claim 1 wherein said liquid core material is awater-miscible material.

6. The method of claim 1 wherein said microcapsules have an averageparticle diameter of between about 0.10 and about 1.0 micron.

7. The method of claim 6 wherein said microcapsules have an averageparticle diameter of between about 0.25 and about 0.8 micron.

8. Microcapsular opacifiers comprising discrete, substantiallyspherical, air-containing microcapsules having substantially continuous,organic, polymeric solid walls, said microcapsules having an averageparticle diameter of below about 1 micron, said air-containingmicrocapsules being capable of increasing the TAPPI opacity of a ream ofbond paper having a TAPPI opacity of 69 percent points without saidair-containing microcapsules, by at least 9 percent points when saidpaper is provided with 3.84 pounds per ream of said air-containingmicrocapsules.

9. Microcapsular opacifiers as defined in claim 8 having an averageparticle diameter of between about .10 and 1.0 micron.

l0. Microcapsular opacifiers as defined in claim 9 having an averageparticle diameter of between about 0.25 and about 0.8 micron.

11. Microcapsular opacifiers as defined in claim 8, wherein said wallscomprise a thermosetting resin.

12. Microcapsular opacifiers as defined in claim 11, wherein saidthermosetting resin is a formaldehyde condensation product.

13. Microcapsular opacifiers as defined in claim 12, wherein saidformaldehyde condensation product is ureaformaldehyde,melamine-formaldehyde or phenol-formaldehyde.

14. Microcapsular opacifiers as defined in claim 13, wherein saidformaldehyde condensation product is ureaformaldehyde.

15. Microcapsular opacifiers as defined in claim 14, said opacifiershaving an average particle diameter of between about 0.25 and about 0.8micron.

16. Microcapsular opacifiers as defined in claim 8, wherein said wallscomprise styrene-maleic anhydride and urea-formaldehyde.

17. Microcapsular opacifiers as defined in claim 8, wherein said wallscomprise a protein.

18. Microcapsular opacifiers as defined in claim 17, wherein said wallscomprise gelatin.

19. A method for the production of air-containing microcapsularopacifiers, which method comprises providing discrete, essentiallyspherical precursor microcapsules by admixing (A) a water-immiscibleoily material;

(B) an amphiphilic emulsifying agent;

(C) at least one solution comprising a polymeric resin,

said solution selected from the group consisting of:

(1) solutions comprising a hydrophobic, thermoplastic resin as thesolute, said resin not having appreciable solubility in the oilymaterial, and a waterand oil-miscible organic liquid as the solvent,said thermoplastic resin being capable of being separated in solidparticle form from solution upon dilution with Water;

(2) solutions compirsing a partially condensed thermosetting resin asthe solute and water as the solvent, said resin condensate being capableof being separated in solid particle form from solution upon dilutionwith water, and

(3) mixtures of (1) and (2); and,

(D) water in a quantity suflicient to cause the separation of at leastone of said polymeric resins from solution,

the sequence of said admixing being such that at least one of thesynthetic resins in the admixture separates from solution in solidparticle form upon dilution with water as the final operation or saidprocess, which dilution takes place slowly and under conditions of briskagitation, said precursor microcapsules having an average particlediameter of below about one micron and containing a liquid corematerial, and heating said precursor microcapsules to a temperaturesufficient to substantially completely drive off said liquid corematerial from said precursor microcapsules and replace said corematerial with air.

20. The method of claim 19 wherein said thermosetting resin is aformaldehyde condensation product.

21. The method of claim 20 wherein the resin is a partially condensedurea-formaldehyde condensate.

22. A method for the production of air-containing microcapsularopacifiers, which method comprises providing discrete, essentiallyspherical precursor microcapsules by the steps of:

(A) forming a primary oil-in-water emulsion, which emulsion comprises awater-immiscible oily material dispersed in the form of microscopicdroplets in a colloidal solution of one or more emulsifying agentshaving about the same hydrophil-lipophil balance as the oily material,and at least one of said emulsifying agents being selected from thegroup consisting of an emulsifying agent possessing cross-linkablegroups and an emulsifying agent possessing complexing sites; and

(B) forming an impermeable coating around said dispersed oil dropletssolely by adding to the emulsion a member selected from the groupconsisting of an aldehyde, polyvinyl alcohol, gelatin, gum tragacanth,ethanolamine, ethylene diamine, sodium borate, and methyl cellulose,said member reacting with the emulsifying agent so as to form animpermeable coating around said dispersed oil droplets which additiontakes place slowly and under conditions of brisk agitation,

said precursor microcapsules having an average particle diameter ofbelow about one micron, and heating said precursor microcapsules to atemperature sufiicient to substantially completely drive off said corematerial from said precursor microcapsules and replace said corematerial with air.

23. A method for the production of air-containing microcapsularopacifiers, which method comprises providing discrete, essentiallyspherical precursor microcapsules having substantially continuous, solidwalls comprising urea-formaldehyde, said microcapsules having an averageparticle diameter of below about one micron and containing mineralspirits as the core material, and heating said microcapsules to atemperature sufiicient to substantially completely drive off said corematerial from said microcapsules and replace said core material withair, said air-containing microcapsules being capable of increasing theTAPPI opacity of a ream of bond paper having a TAPPI opacity of 69percent points without said aircontaining microcapsules, by at least 9percent points when said paper is provided with 3.84 pounds per ream ofsaid air-containing microcapsules.

References Cited UNITED STATES PATENTS 2,797,201 6/1957 Veatch et a1.260-25 2,929,106 3/ 1960 Snow 264-96X 3,137,631 6/1964 Soloway 424-16X3,161,468 12/1964 Walsh 252-449X 3,330,784 7/1967 Anspon 260-253,418,656 12/1968 Vassiliades 252-316 3,516,941 6/1970 Matson.

RICHARD D. LOVERING, Primary Examiner U.S. Cl. X.R.

Notice of Adverse Decision in Interference In Interference No. 100,953,involving Patent No. 3,585,149, A. E. Vassiliades, E. F. Nauman and S.Shroff, MICROCAPSULAR OPACIFIER SYSTEM, final judgement adverse to thepatentees was rendered Jan. 25, 1985, as to claims 1 and 8.

[Official Gazette September I 7. 1985.]

